The present invention relates to a method and circuit arrangement for determining displacements of scene elements between successively transmitted image sequences corresponding to a field or frame. Such scene elements are associated with moving objects appearing in the scene depicted by the image sequences. Such a method is described by Hans C. Bergmann in an article entitled "Analysis of Different Displacement Estimation Algorithms for Digital Television Signals," published in NATO ASI Series, Vol. F2, Image Sequence Processing and Dynamic Scene Analysis, edited by T. S. Huang, published by Springer Verlag, Berlin, Heidelberg, 1983, at pages 215-234.
Various recursive and nonrecursive estimating methods have been published for determination of displacement in television signals under real-time conditions.
Nonrecursive methods are disclosed, for example, by Schalkoff in "IEEE Trans. on Pattern Analysis and Machine Intelligence," Vol. 4, No. 1, January, 1982, at pages 2-10. They have the advantage that hardware implementation thereof is relatively easy but they operate with sufficient accuracy in their estimation only for displacements of up to 2 pixels per frame. See, in this connection, Bergmann, supra, page 222. Since displacements of more than 10 pixels per frame occur in natural television image sequences, these methods find only limited use.
Recursive estimating methods are generally based on an optimization criterion, with a correction value being added to the respectively preceding estimated value so that the optimization value gradually approaches the optimum value. Examination of known recursive displacement estimation methods has shown that they converge at sufficient speed, i.e. already after a few recursion steps, for average displacements up to about 4 pixels per frame. However, for large displacements up to 20 pixels per frame, five and more recursion steps are required to overcome the transient state.
However, with respect to real-time estimation, the number of recursion steps is limited to one or two steps so that these methods likewise find only limited use for the estimation of large displacements.